Controller for a fluid cylinder

ABSTRACT

A device is disclosed for controlling a double action working cylinder (10) having a piston (11) with a piston rod (12) on a single side by means of a multiple-way valve (19), in which the available forces are to be fully applied at the beginning of the extension of the piston rod (12) and the differential motion becomes effective after a fixed distance of displacement of the piston. The multiple-way valve (19) has seven connection openings (T1, A1, P, B1, A2, T2, B2) for driving the predetermined functions, which can be driven in the individual working position by means of a valve piston (20) provided with seven control edges (1-7).

BACKGROUND OF THE INVENTION

The invention relates to an apparatus for controlling a double-actingworking cylinder having a piston with one-sided piston rod by means of amultiway valve, which supplies the working medium to one of thedifferently sized swept volumes of the working cylinder, respectively,and permits it to flow out of the other swept volume during the pistonstroke. The multiway valve, which is designed in the manner of a pistonvalve, has a pump connection P, a connection A1 for an inflow andoutflow line between the large swept volume of the working cylinder andthe multiway valve, a connection B1 for an inflow and outflow linebetween the small swept volume of the working cylinder and the multiwayvalve, a connection A2 for a connecting line connected to the inflow andoutflow line positioned between connection A1 and the large swept volumeof the working cylinder, and two reservoir connections T1, T2. The valvepiston of the multiway valve has at least five control edges disposed onring collars and the connections P, A1, A2, B1, T1, T2 are disposed insuch a way that as the piston is extended, to use the differentialaction of the working cylinder with rapid piston motion, the inflow andoutflow line is connectable with connection A2 and, as the piston isretracted, connection A1 is connectable with T1 and connection A2 withT2.

DE 30 00 260 C2 describes an apparatus with the aforementionedcharacteristics. The circuit arrangement disclosed therein with anassignment of six connections in series of the multiway valve employedis intended on the one hand to permit travel of the working cylinderpiston with differential action, i.e., with rapid piston stroke, and onthe other hand to ensure as compact a structural design of the multiwayvalve as possible with uniform pressurization of the five control edgesprovided on the multiway valve with the same quantity of working mediumin both travel directions of the piston of the working cylinder.

For this purpose, in the known apparatus, as the working cylinder pistonis extended, the additional connection opening connected to the largeswept volume of the working cylinder via the connecting line, isconnected via an associated control edge, which controls only the flowof working medium passing through this connecting line, with the lineacting as the outflow from the small swept volume. Simultaneously, viaanother control edge and thus independently from the flow path betweenthe swept volumes of the working cylinder, the pump connection isconnected with the inlet to the large swept volume of the workingcylinder. At the same time, as the piston of the working cylinder isretracted, the connection with the reservoir can be established throughan additional connection provided in the multiway valve.

In addition, the interposition of a separate directional control valvemakes it possible on the one hand to adjust the forward motion of theworking cylinder piston using the differential action of the cylinder,while on the other hand using the full force in the extended endposition of the piston rod. For this purpose, in the extended positionof the piston rod, the small swept volume of the working cylinder isconnected to the reservoir, whereby in the corresponding switchingposition of the directional control valve, the pressure acting on thelarge area of the piston of the working cylinder is no longercounteracted by a pressure in the small swept volume of the workingcylinder such that the holding force is doubled compared to the stateexisting during extension of the piston rod.

First, the known embodiment only addresses the switching that permitsthe full force to act when the piston rod is extended. Moreover, thereis the particular disadvantage that the additional directional controlvalve adds complexity to the corresponding design of the controlapparatus. This is particularly true because the directional controlvalve must be designed for the same rated quantity as the multiwayvalve, which serves for the main control of the working cylinder, sincethe addressed functional case of connecting the small swept volume withthe reservoir requires the same flow of working medium to be directedthrough the directional control valve as through the multiway valve.

SUMMARY OF THE INVENTION

Thus, it is the object of the invention to make it possible in a controlapparatus for a differential cylinder with the initially mentionedcharacteristics, while eliminating an additional directional controlvalve, to adjust the full force acting on the piston of the workingcylinder even at the start of the extension motion of the piston rodand, if a predefined piston stroke in the working cylinder is exceeded,to adjust the differential motion with rapid piston motion.

The invention is based on the fact that an additional connection B2 isprovided for an additional connecting line connected to the inflow andoutflow line located between connection B1 and the small swept volume ofthe working cylinder and, to control the two connections of the workingcylinders, seven control edges are formed on the valve piston and areassigned to the seven connections P, A1, A2, B1, B2, T1, T2 of themultiway valve such that, at the beginning of the extension motion ofthe piston rod, the inflow and outflow line connected to the small sweptvolume of the working cylinder is connected with a reservoir connectionT1 or T2 and, after traveling past the valve-piston positioncorresponding to the set start of the differential motion effective overthe rest of the extension motion of the piston rod upon reaching apredefined piston position within the working cylinder, the connectionbetween the inflow and outflow line and the reservoir connection T1 orT2 is blocked and the connection between the inflow and outflow line andconnection A2 is opened.

The advantage of the invention is that forming an additional seventhconnection opening in the multiway valve itself and adapting the designof the valve piston to include seven control edges makes it possible toeliminate an additional directional control valve, since the function ofthe directional control valve, both with respect to forming anadditional reservoir connection and with respect to the instant when theadditional reservoir connection is blocked for the differential motionof the piston, is integrated in the multiway valve itself. While theprior art multiway valve has five control edges for controlling the twoconnections of the working cylinder, the multiway valve according to theinvention is distinguished by seven control edges formed on the valvepiston. These control edges become active, respectively, in threedifferent valve-piston positions, namely in a first position duringretraction of the piston rod and in a second and third positiongraduated over the path of the piston within the working cylinder duringextension of the piston rod. This additional seventh connection openingincreases the size of the multiway valve only insignificantly.

According to a first exemplary embodiment of the invention, the multiwayvalve has seven openings P, A1, A2, B1, B2, T1, T2, which communicate,respectively, with a ring channel. Starting at the non-blocked valveend, opening T1 leads to the reservoir, A1 to the large swept volume, Pto the pump, B1 to the small swept volume, A2 to the connecting line, T2to the reservoir, and B2 to the connecting line. In the central positionof the valve piston, the ring collars are assigned in blocking functionto each second opening A1, B1, A2 and the associated ring channel. Inthe central position of the valve piston, the outlying openings B2 areopen to opening T2 and, during extension of the piston rod, uponreaching the valve-piston position corresponding to the predefined startof the differential motion, are blocked to opening T2 by the associatedcontrol edge. In the defined sequence of the connection openings in themultiway valve, the change in the switching of the connection openingsrequired in the second and third valve-piston position over the path ofthe piston within the working cylinder is implemented, in particular, byinitially connecting the small swept volume of the working cylinder witha reservoir connection via connection opening B2, while blocking thisconnection during extension of the piston rod at the instant when thestart of the differential motion is reached.

An alternative embodiment of the multiway valve provides that themultiway valve has seven openings P, A1, A2, B1, B2, T1, T2communicating, respectively, with a ring channel. In the centralvalve-piston position, the ring collars are assigned to each secondopening and the associated ring channel. Starting at the non-blockedvalve end, opening T1 leads to the reservoir, A1 to the large sweptvolume, P to the pump, B1 to the small swept volume, T2 to thereservoir, A2 to the connecting line, and B2 to the connecting line. Thevalve piston has four ring collars. In the central position of the valvepiston, three of these ring collars are assigned in blocking function toopenings A1, B1, A2 and the associated ring channel. The fourth pistoncollar is assigned to opening T2 and is arranged and designed in such away that in the central valve-piston position, on the one hand, theopening T2 is open to connection B1 and, during extension of the pistonrod, upon reaching the valve-piston position corresponding to thedefined start of the differential motion, is blocked toward opening B1.On the other hand, in the valvepiston position corresponding to theretraction of the piston rod, the connection of openings T2 and A2 isopen. This alternative embodiment is based on a changed sequence of theconnection openings. This is why four ring collars are formed on thevalve piston. The fourth ring collar is uniquely assigned to connectionT2 and is designed in such a way that initially, an open connectionbetween the small swept volume of the working cylinder and a reservoirconnection is established via connection B1. As the valve piston shifts,this connection is blocked on reaching the start of the desireddifferential motion. At the same time, the fourth piston collarcontinues to leave open connection T2 in the direction of theneighboring connection A2 such that the eighth control edge, which isgiven per se with four ring collars, does not become functionallyeffective. Instead, this embodiment has also seven active control edges.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawing depicts exemplary embodiments of the invention, which aredescribed in further detail below.

FIG. 1 shows a hydraulic circuit diagram for controlling a differentialcylinder including the switching of the multiway valve, which isprovided with seven connection openings.

FIG. 2 shows the subject of FIG. 1 in a different embodiment.

DETAILED DESCRIPTION OF THE INVENTION

For the following functional explanation, the drawing shows only theinitial position to give a rough indication and does not take intoaccount the scale of the openings and the ring collars. It is left tothe person of average skill in the art to define the design layout andselect the dimensions knowing the functional interrelationships intendedby the invention.

The differential cylinder comprises a working cylinder 10 and a piston11 sliding therein, which has different areas on its two sides, and apiston rod 12. Piston 11 separates the working cylinder 10 into a largeswept volume 13 and a small swept volume 14. Each swept volume 13, 14 isprovided at its end with a respective inflow and, simultaneously,outflow line 15 and 16 for the working medium hereinafter referred to asoil by way of example. The oil is located in a reservoir 17 (depicted inseparate parts) and is assigned to a multiway valve 19 by means of apump 18. From there, depending on the position of the valve piston 20,it flows to differential cylinder 10 or, through connected outlet lines,to reservoir 17. Elements that are not crucial for the understanding ofthe invention, such as pressure control valves, one-way restrictors, orthe like, are not depicted.

In the embodiment shown in FIG. 1, multiway valve 19 has seven openingsin a row, T1, A1, P, B1, T2, A2, B2. These openings are connected inthis sequence with reservoir 17, inflow and outflow line 15 leading tothe large swept volume, pump 18, inflow and outflow line 16 of aconnecting line 22, which opens out into line 15, leading to the smallswept volume 14, again reservoir 17, and an additional connecting line23 opening out into inflow and outflow line 16. In the shown centralposition of valve piston 20 (zero position) within the indicated valvehousing, pass into associated ring channels. In the zero position, thesering channels are blocked or open, respectively, by ring collars 21formed on valve piston 20 in a manner to be described below.

In the depicted zero position, connections A1, B1, and T2 are blocked bythe three ring collars 21 of valve piston 20. At the same time, endcollar 25 of valve piston 20, which partially blocks connection B2,leaves open a flow path 26 to connection T2 blocked in zero position bythe associated ring collar 21. The size of the flow path 26 effected bythe lacking overlap of end collar 25 with connection B2 is a function ofthe length of the piston stroke of piston 11 within working cylinder 10,after the completion of which the differential motion of the piston 11is to begin.

If valve piston 20 is displaced toward the left, on the one handconnections A1 and P are simultaneous unblocked or connected while onthe other hand connection T2 is opened to connection B2, which in turn,due to the position of end collar 25, initially still leaves flow path26 open. During this segment of the path traveled by valve piston 20,the pump pressurizes the large swept volume 13 of working cylinder 10via connection A1 and inflow and outflow line 15. An open connectionexists between the small swept volume 14 of working cylinder 10 and thereservoir connection T2 through inflow and outflow line 16 andconnecting line 23 branching off therefrom and leading to connection B2,such that the pressure acting on the large area of piston 11 is nolonger counteracted by a pressure in the small swept volume 14. Once theinstant of the start of the differential motion determined by the valvepiston design is reached during the piston stroke of piston 11 withinworking cylinder 10, the end collar 25 of valve piston 20 blocksconnection B2 with the associated control edge 5. At the same time,connection B1 is connected with connection A2. As a result, the oildisplaced from the small swept volume 14 as piston A1 continues to moveis supplied via inflow and outflow line 16 and connection B1 toconnection A2 and from there via connecting line 22 of the inflow andoutflow line 15 to the large swept volume 13. Consequently, during thedifferential motion of piston 11 within working cylinder 10, pump 18needs to deliver only half the quantity of working medium with respectto the large swept volume 13.

If valve piston 20, starting from the zero position depicted in FIG. 1,is displaced towards the right, it is also ensured that the deliveryrate of pump 18 remains unchanged when the piston rod is retracted. Onthe supply side, this has the result of connecting connections P, B1 tothe small swept volume 14 via inflow and outflow line 16, while thelarge swept volume 13 is connected with T1 via the inflow and outflowline and connection A1, which is blocked against P, and with T2 viaconnecting line 22 branching off from inflow and outflow line 15 andconnection A2. To this extent, this results in a partitioning of the oilquantity flowing out of the large swept volume 13.

The exemplary embodiment depicted in FIG. 2 is distinguished from theabove described embodiment in that, in the sequence of the connectinglines, connections T2 and A2 are interchanged with respect to theembodiment depicted in FIG. 1. Thus, connection B1 is now next to T2 andconnection A2 is next to B2. Due to this interchange of the connectionopenings, connections A1, B1, and A2 are now blocked in the depictedzero position by the three ring collars 21 of valve position 20. Inaddition, a fourth piston collar 24 is formed on valve piston 20 andassigned to connection T2 in such a way that in the central position ofvalve piston 20 (zero position), ring collar 24 effects the functionallyequivalent open flow path 26 toward connection B1. At the same time, itis ensured that connection T2 is not blocked in the direction ofconnection A2 in any position of valve piston 20.

If valve piston 20 is shifted leftward in this embodiment, connectionsA1 and P are unblocked. At the same time, connection B1 is opened, whichestablishes the connection with T2 via the still open flow path 26. Asdescribed with respect to the embodiment according to FIG. 1, thepressurization of the large swept volume 13 of working cylinder 10causes the piston rod to extend. At the start of this extension motion,the small swept volume 14 of working cylinder 10 is connected withconnection T2 via line 16, connection B1, and the still open flow path26 such that the small swept volume 14 of working cylinder 10 ispressureless. If valve piston 20 continues to shift leftward, theconnection between B1 and T2 is blocked by control edge 5 of the fourthpiston collar 24. At the same time, the connection between B2 and A2,which are positioned next to each other, is opened. As a result, the oildisplaced from the small swept volume 14 during the extension of pistonrod 12 is fed via line 16 and connecting line 23 branching offtherefrom, the connected connections B2, A2, and connecting line 22linked to A2 into the inflow and outflow line 15 to the large sweptvolume 13 of working cylinder 10.

Shifting valve piston 20 towards the right, starting from the centralposition of the valve piston according to FIG. 2, causes a connection ofP, B1, through which the small swept volume 14 of working cylinder 10 ispressurized with oil. The oil flowing out of the large swept volume 13of working cylinder 10 distributes itself through lines 15 and 22 toconnections A1 and A2. From here, it can flow off to the reservoir viathe connection with T1, T2 created by the position of valve piston 20,which is shifted toward the right. Since the fourth piston collar 24 isdesigned in such a way that connection T2 is not blocked in thedirection of A2 in any position of valve piston 20, the desiredconnection from A2 to T2 is given.

The characteristics of the subject of this document disclosed in theabove specification, the claims, the abstract, and the drawing can besignificant either individually or in any combination for theimplementation of the invention in its various embodiments.

What is claimed is:
 1. A controller for a double-acting fluid cylinderhaving a working piston movable in a forward direction by a first fluidvolume, and in a rearward direction by a second fluid volume, saidcylinder being operable by said controller under a source of fluidpressure having an associated fluid reservoir, and said controllercomprising a multi-position flow control valve comprising:a plurality ofsequentially arranged fluid ports including a pressure port (P) coupledin fluid communication with said source of fluid pressure, a firstreversing port (A1) coupled in fluid communication with said first fluidvolume of said cylinder and couplable in fluid communication with saidport P, a second reversing-port (B1) coupled in fluid communication withsaid second fluid volume of said cylinder and couplable in fluidcommunication with said port P, a first by-pass port (A2) coupled influid communication with said first fluid volume of said cylinder andcouplable in fluid communication with said port B1, a second by-passport B2 coupled in fluid communication with said second fluid volume ofsaid cylinder, a first reservoir port (T1) coupled in fluidcommunication with said reservoir and couplable in fluid communicationwith said port A1, and a second reservoir port (T2) coupled in fluidcommunication with said reservoir and couplable in fluid communicationwith said port B2; and a valve positioner having a plurality of valveelements including, in series, a first valve element, a second valveelement, a third valve element, and a fourth valve element, whereby saidvalve positioner is displaceable from a null position wherein said portA1 is blocked by said first valve element, said port B1 is blocked bysaid second valve element, and said port T2 is blocked by said thirdvalve element, to a first control position wherein said first valveelement is displaced from said port A1 opening said port A1 in fluidcommunication with said port P admitting fluid pressure to said firstfluid volume of said cylinder moving said working piston in said forwarddirection, said fourth valve element is at least partially displacedfrom said port B2 opening said port B2, and said third valve element isdisplaced from said port T2 opening said port T2 in fluid communicationwith said port B2 admitting fluid displaced from said second fluidvolume into said reservoir, and whereby said valve positioner is furtherdisplaceable from said first control position to a second controlposition wherein said second valve element is displaced from said portB1 opening said port B1 in fluid communication with said port A2admitting fluid displaced from said second fluid volume into said firstfluid volume, and said port B2 is blocked by said fourth valve elementclosing fluid communication between said port B2 and said port T2. 2.The controller of claim 1 wherein in said null position said fourthvalve element is at least partially displaced from said port B2 openingsaid port B2.
 3. The controller of claim 1 wherein said port A2 furtheris couplable in fluid communication with said port T2, and wherein saidvalve positioner further is displaceable from said null position to athird control position wherein said second valve element is displacedfrom said port B1 opening said port B1 in fluid communication with saidport P admitting fluid pressure to said second fluid volume of saidcylinder moving said working piston in said rearward direction, saidfirst valve element is displaced from said port A1 opening said port A1in fluid communication with said port T1 admitting a first partitionedquantity of fluid displaced from said first fluid volume into saidreservoir, and said third valve element is displaced from said port T2opening said port T2 in fluid communication with said port A2 admittinga second partitioned quantity of fluid displaced from said first fluidvolume of said cylinder into said reservoir.
 4. The controller of claim1 wherein said control valve further comprises a valve channel, each ofsaid fluid ports opening in linear succession into fluid communicationwith said valve channel, and said valve positioner being configured as avalve piston which is slidably received within said valve channel forlinear movement from said first control position to said second controlposition.
 5. The controller of claim 4 wherein said fluid ports arearranged successively in the order of T1, A1, P, B1, A2, T2, and B2. 6.The controller of claim 1 wherein said first fluid volume of saidcylinder is larger than said second fluid volume.
 7. The controller ofclaim 1 wherein said working piston of said cylinder defines a firstarea on the side of said first fluid volume and a second area on theside of said second fluid volume, said first area being larger than saidsecond area.
 8. A fluid power system comprising:a double-acting fluidcylinder having a working piston movable in a forward direction by afirst fluid volume, and in a rearward direction by a second fluidvolume; a fluid pressure source for providing working fluid pressure tosaid cylinder; a fluid reservoir for supplying working fluid to saidfluid pressure source; and a controller for operating said cylinderunder said working fluid pressure, said controller comprising amulti-position flow control valve comprising:a plurality of sequentiallyarranged fluid ports including a pressure port (P) coupled in fluidcommunication with said source of fluid pressure, a first reversing port(A1) coupled in fluid communication with said first fluid volume of saidcylinder and couplable in fluid communication with said port P, a secondreversing port (B1) coupled in fluid communication with said secondfluid volume of said cylinder and couplable in fluid communication withsaid port P, a first by-pass port (A2) coupled in fluid communicationwith said first fluid volume of said cylinder and couplable in fluidcommunication with said port B1, a second by-pass port B2 coupled influid communication with said second fluid volume of said cylinder, afirst reservoir port (T1) coupled in fluid communication with saidreservoir and couplable in fluid communication with said port A1, and asecond reservoir port (T2) coupled in fluid communication with saidreservoir and couplable in fluid communication with said port B2; and avalve positioner having a plurality of valve elements including, inseries, a first valve element, a second valve element, a third valveelement, and a fourth valve element, whereby said valve positioner isdisplaceable from a null position wherein said port A1 is blocked bysaid first valve element, said port B1 is blocked by said second valveelement, and said port T2 is blocked by said third valve element, to afirst control position wherein said first valve element is displacedfrom said port A1 opening said port A1 in fluid communication with saidport P admitting fluid pressure to said first fluid volume of saidcylinder moving said working piston in said forward direction, saidfourth valve element is at least partially displaced from said port B2opening said port B2, and said third valve element is displaced fromsaid port T2 opening said port T2 in fluid communication with said portB2 admitting fluid displaced from said second fluid volume into saidreservoir, and whereby said valve positioner is further displaceablefrom said first control position to a second control position whereinsaid second valve element is displaced from said port B1 opening saidport B1 in fluid communication with said port A2 admitting fluiddisplaced from said second fluid volume into said first fluid volume,and said port B2 is blocked by said fourth valve element closing fluidcommunication between said port B2 and said port T2.
 9. The fluid powersystem of claim 8 wherein in said null position of said flow controlvalve said fourth valve element of said valve positioner is at leastpartially displaced from said port B2 opening said port B2.
 10. Thefluid power system of claim 8 wherein said port A2 of said flow controlvalve further is couplable in fluid communication with said port T2, andwherein said valve positioner further is displaceable from said nullposition to a third control position wherein said second valve elementis displaced from said port B1 opening said port B1 in fluidcommunication with said port P admitting fluid pressure to said secondfluid volume of said cylinder moving said working piston in saidrearward direction, said first valve element is displaced from said portA1 opening said port A1 in fluid communication with said port T1admitting a first partitioned quantity of fluid displaced from saidfirst fluid volume into said reservoir, and said third valve element isdisplaced from said port T2 opening said port T2 in fluid communicationwith said port A2 admitting a second partitioned quantity of fluiddisplaced from said first fluid volume of said cylinder into saidreservoir.
 11. The fluid power system of claim 8 wherein said controlvalve further comprises a valve channel, each of said fluid portsopening in linear succession into fluid communication with said valvechannel, and said valve positioner being configured as a valve pistonwhich is slidably received within said valve channel for linear movementfrom said first control position to said second control position. 12.The fluid power system of claim 11 wherein said fluid ports are arrangedsuccessively in the order of T1, A1, P, B1, A2, T2, and B2.
 13. Thefluid power system of claim 8 wherein said first fluid volume of saidcylinder is larger than said second fluid volume.
 14. The fluid powersystem of claim 8 wherein said working piston of said cylinder defines afirst area on the side of said first fluid volume and a second area onthe side of said second fluid volume, said first area being larger thansaid second area.
 15. A controller for a double-acting fluid cylinderhaving a working piston movable in a forward direction by a first fluidvolume, and in a rearward direction by a second fluid volume, saidcylinder being operable by said controller under a source of fluidpressure having an associated fluid reservoir, and said controllercomprising a multi-position flow control valve comprising:a plurality ofsequentially arranged fluid ports including a pressure port (P) coupledin fluid communication with said source of fluid pressure, a firstreversing port (A1) coupled in fluid communication with said first fluidvolume of said cylinder and couplable in fluid communication with saidport P, a second reversing port (B1) coupled in fluid communication withsaid second fluid volume of said cylinder and couplable in fluidcommunication with said port P, a first by-pass port (A2) coupled influid communication with said first fluid volume of said cylinder, asecond by-pass port B2 coupled in fluid communication with said secondfluid volume of said cylinder and couplable in fluid communication withsaid port A2, a first reservoir port (T1) coupled in fluid communicationwith said reservoir and couplable in fluid communication with said portA1, and a second reservoir port (T2) coupled in fluid communication withsaid reservoir and couplable in fluid communication with said port B1;and a valve positioner having a plurality of valve elements including,in series, a first valve element, a second valve element, a third valveelement, and a fourth valve element, whereby said valve positioner isdisplaceable from a null position wherein said port A1 is blocked bysaid first valve element, said port B1 is blocked by said second valveelement, said third valve element is positioned to open said port T2,and said port A2 is blocked by said fourth valve element, to a firstcontrol position wherein said first valve element is displaced from saidport A1 opening said port A1 in fluid communication with said port Padmitting fluid pressure to said first fluid volume of said cylindermoving said working piston in said forward direction, and said secondvalve element is displaced from said port B1 opening said port B1 influid communication with said port T2 admitting fluid displaced fromsaid second fluid volume into said reservoir, and p1 whereby said valvepositioner is further displaceable from said first control position to asecond control position wherein said third valve element is displacedfrom said port T2 closing fluid communication between said port T2 andsaid port B1, and said fourth valve element is displaced from said portA2 opening said port A2 in fluid communication with said port B2admitting fluid displaced from said second fluid volume into said firstfluid volume.
 16. The controller of claim 15 wherein said port T2 isopened in a direction of fluid communication with said port A2, andwherein said valve positioner further is displaceable from said nullposition to a third control position wherein said second valve elementis displaced from said port B1 opening said port B1 in fluidcommunication with said port P admitting fluid pressure to said secondfluid volume of said cylinder moving said working piston in saidrearward direction, said first valve element is displaced from said portA1 opening said port A1 in fluid communication with said port T1admitting a first partitioned quantity of fluid displaced from saidfirst fluid volume into said reservoir, and said fourth valve element isdisplaced from said port A2 opening said port A2 in fluid communicationwith said port T2 admitting a second partitioned quantity of fluiddisplaced from said first fluid volume of said cylinder into saidreservoir.
 17. The controller of claim 15 wherein said control valvefurther comprises a valve channel, each of said fluid ports opening inlinear succession into fluid communication with said valve channel, andsaid valve positioner being configured as a valve piston which isslidably received within said valve channel for linear movement fromsaid first control position to said second control position.
 18. Thecontroller of claim 17 wherein said fluid ports are arrangedsuccessively in the order of T1, A1, P, B1, T2, A2, and B2.
 19. Thecontroller of claim 15 wherein said first fluid volume of said cylinderis larger than said second fluid volume.
 20. The controller of claim 15wherein said working piston of said cylinder defines a first area on theside of said first fluid volume and a second area on the side of saidsecond fluid volume, said first area being larger than said second area.21. A fluid power system comprising:a double-acting fluid cylinderhaving a working piston movable in a forward direction by a first fluidvolume, and in a rearward direction by a second fluid volume; a fluidpressure source for providing working fluid pressure to said cylinder; afluid reservoir for supplying working fluid to said fluid pressuresource; and a controller for operating said cylinder under said workingfluid pressure, said controller comprising a multi-position flow controlvalve comprising:a plurality of sequentially arranged fluid portsincluding a pressure port (P) coupled in fluid communication with saidsource of fluid pressure, a first reversing port (A1) coupled in fluidcommunication with said first fluid volume of said cylinder andcouplable in fluid communication with said port P, a second reversingport (B1) coupled in fluid communication with said second fluid volumeof said cylinder and couplablc in fluid communication with said port P,a first by-pass port (A2) coupled in fluid communication with said firstfluid volume of said cylinder, a second by-pass port B2 coupled in fluidcommunication with said second fluid volume of said cylinder andcouplable in fluid communication with said port A2, a first reservoirport (T1) coupled in fluid communication with said reservoir andcouplable in fluid communication with said port A1, and a secondreservoir port (T2) coupled in fluid communication with said reservoirand couplable in fluid communication with said port B1; and a valvepositioner having a plurality of valve elements including, in series, afirst valve element, a second valve element, a third valve element, anda fourth valve element, whereby said valve positioner is displaceablefrom a null position wherein said port A1 is blocked by said first valveelement, said port B1 is blocked by said second valve element, saidthird valve element is positioned to open said port T2, and said port A2is blocked by said fourth valve element, to a first control positionwherein said first valve element is displaced from said port A1 openingsaid port A1 in fluid communication with said port P admitting fluidpressure to said first fluid volume of said cylinder moving said workingpiston in said forward direction, and said second valve element isdisplaced from said port B1 opening said port B1 in fluid communicationwith said port T2 admitting fluid displaced from said second fluidvolume into said reservoir, and whereby said valve positioner is furtherdisplaceable from said first control position to a second controlposition wherein said third valve element is displaced from said port T2closing fluid communication between said port T2 and said port B1, andsaid fourth valve element is displaced from said port A2 opening saidport A2 in fluid communication with said port B2 admitting fluiddisplaced from said second fluid volume into said first fluid volume.22. The fluid power system of claim 21 wherein said port T2 of saidcontrol valve is opened in a direction of fluid communication with saidport A2, and wherein said valve positioner further is displaceable fromsaid null position to a third control position wherein said second valveelement is displaced from said port B1 opening said port B1 in fluidcommunication with said port P admitting fluid pressure to said secondfluid volume of said cylinder moving said working piston in saidrearward direction, said first valve element is displaced from said portA1 opening said port A1 in fluid communication with said port T1admitting a first partitioned quantity of fluid displaced from saidfirst fluid volume into said reservoir, and said fourth valve element isdisplaced from said port A2 opening said port A2 in fluid communicationwith said port T2 admitting a second partitioned quantity of fluiddisplaced from said first fluid volume of said cylinder into saidreservoir.
 23. The fluid power system of claim 21 wherein said controlvalve further comprises a valve channel, each of said fluid portsopening in linear succession into fluid communication with said valvechannel, and said valve positioner being configured as a valve pistonwhich is slidably received within said valve channel for linear movementfrom said first control position to said second control position. 24.The fluid power system of claim 23 wherein said fluid ports are arrangedsuccessively in the order of T1, A1, P, B1, T2, A2, and B2.
 25. Thefluid power system of claim 21 wherein said first fluid volume of saidcylinder is larger than said second fluid volume.
 26. The fluid powersystem of claim 21 wherein said working piston of said cylinder definesa first area on the side of said first fluid volume and a second area onthe side of said second fluid volume, said first area being larger thansaid second area.